71 lines
2.3 KiB
Python
71 lines
2.3 KiB
Python
"""Implement a tiny subset of dataclasses_json for config."""
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from collections.abc import Mapping, Sequence
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from dataclasses import asdict, fields, is_dataclass
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from typing import Any, Dict, Type
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class DataClassJsonMixin:
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"""Adds from_dict to dataclass."""
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@classmethod
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def from_dict(cls, data: Dict[str, Any]) -> Any:
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"""Parse dataclasses recursively."""
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kwargs: Dict[str, Any] = {}
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cls_fields = {field.name: field for field in fields(cls)}
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for key, value in data.items():
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if key not in cls_fields:
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# Skip unknown fields
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continue
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field = cls_fields[key]
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if is_dataclass(field.type):
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assert issubclass(field.type, DataClassJsonMixin), field.type
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kwargs[key] = field.type.from_dict(value)
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else:
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kwargs[key] = _decode(value, field.type)
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# Fill in optional fields with None
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for field in cls_fields.values():
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if (field.name not in kwargs) and _is_optional(field.type):
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kwargs[field.name] = None
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return cls(**kwargs)
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def to_dict(self) -> Dict[str, Any]:
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"""Alias for asdict."""
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return asdict(self)
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def _decode(value: Any, target_type: Type) -> Any:
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"""Decode value using (possibly generic) type."""
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if is_dataclass(target_type):
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assert issubclass(target_type, DataClassJsonMixin), target_type
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return target_type.from_dict(value) if value is not None else None
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if hasattr(target_type, "__args__"):
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# Optional[T]
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if type(None) in target_type.__args__:
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optional_type = target_type.__args__[0]
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return _decode(value, optional_type)
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# List[T]
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if isinstance(value, Sequence):
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list_type = target_type.__args__[0]
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return [_decode(item, list_type) for item in value]
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# Dict[str, T]
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if isinstance(value, Mapping):
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value_type = target_type.__args__[1]
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return {
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map_key: _decode(map_value, value_type)
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for map_key, map_value in value.items()
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}
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return value
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def _is_optional(target_type: Type):
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"""True if type is Optional"""
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return hasattr(target_type, "__args__") and (type(None) in target_type.__args__)
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